As social infrastructure, equipment such as water and wastewater systems, high-pressure chemistry pipelines for gas, petroleum and the like, high-speed railways, long big bridges, superhigh-rise buildings, large passenger aircrafts, and vehicles is built. One of important members in the equipment is pipes for passing a fluid such as gas or water. There is a case that pipes are broken due to deterioration or a natural disaster. When pipes are broken and the fluid leaks out, a broken part is required to be repaired. For this purpose, leak of the fluid in the pipes is required to be detected. Hereinbelow, an inspection of the presence/absence of a leak of a fluid in pipes will be called a leak inspection.
A general leak inspection is an auditory sensory inspection of listening to a leak sound by a person. In many cases, however, pipes are arranged under the ground or at a high place, so that an inspection by manpower involves a risk and great effort. To address the problem, devices performing a leak inspection have been proposed.
A leak inspection device described in PTL1 detects a leak by converting a sound detected around a pipe to an electric signal and analyzing the electric signal. The device splits the electric signal acquired from the obtained sound into signals with different frequencies by using a plurality of band-pass filters. The amplitude of an electric signal at each frequency is compared with a threshold. When the amplitude of the electric signal exceeds the threshold in all of the plurality of signals, a leak is determined.
A device described in PTL2 determines the presence/absence of a water leak from the ratio between the number of counts that a vibration level of a pipe due to a water leak exceeds a determination level and the number of counts where the vibration level is less than the determination level.
A device described in PTL3 detects the presence/absence of a water leak by using detection signals acquired by underwater microphones installed at both ends of an inspection section. In the method, the presence/absence of a water leak is determined by generating a composite waveform obtained by adding waveforms having high correlation function of signals detected in temporary sound source positions which are set.
A device described in PTL4 acquires vibrations for predetermined time in a plurality of places using a synchronization signal as a measurement start reference and determines the presence/absence of a water leak.